Turkish Prime Minister Recep Tayyip Erdogan on Thursday gave demonstrators occupying a park in central Istanbul an ultimatum: Leave or be forced out.

“We will no longer wait and see,” he was quoted as saying by Turkish media.

He spoke of a “final warning” after earlier announcing that the police would no longer tolerate the protest camp in Taksim Square’s Gezi Park.

Protests began two weeks ago against a building project planned in the park. A police crackdown prompted demonstrations in other cities and widespread criticism of Mr. Erdogan, whom demonstrators accuse of seeking to impose Islamic values on a secular state.

Mr. Erdogan’s ultimatum was delivered a day after he met with a group of artists, scientists and publicists in Ankara over the development planned for Gezi Park, after which a spokesman for Mr. Erdogan’s party said the government could consider a referendum on the project. A replica of an Ottoman-era military barracks is planned, and it is to house apartments, stores and a museum.

The referendum on whether to go ahead with the development or preserve the park could be decided by voters in Istanbul or residents living near Gezi Park, the spokesman said, but demonstrators Thursday reacted coolly to the idea.

Such a vote would not resolve the dispute over fundamental human rights and personal freedoms in Turkey, they said.

Numerous government officials have stressed that the protesters’ occupation of the park and square could not continue. While the situation there was calm on Thursday, police were out in force, and at least eight water cannon were moved onto the square, witnesses said.

Police use of tear gas, water cannon and batons on protesters has brought international criticism. More protests against Mr. Erdogan were held overnight on Taksim Square, but police did not move in.

Daily demonstrations and near-daily police operations against them have occurred in Ankara, where police overnight used smoke grenades to try to disperse protesters.